1. Technical Field
The present invention relates to a device for measuring physical state in a patient based on the condition of circulation. More specifically, the present invention relates to a health management device for monitoring the user's state of health based on information obtained from the condition of circulation in the user's body, and to an exercise support device which provides appropriate suggestions and guidance to the user, or provides an exercise plan deemed appropriate to create a state of health in the user.
2. Background of the Invention
With the rapid aging of society in recent years, the health issues of middle aged and elderly persons, geriatric diseases being chief among these, have been a topic of much discussion. Various factors have been cited as causes of such diseases. As one example of these factors, evidence has been found which suggests that insufficient circulation can cause health problems. When circulation is insufficient, cells and tissues do not receive the necessary amount of oxygen and nutrients. When this situation persists for a long period of time, organic pathological changes begin to occur in organs and tissues. Once these changes have progressed to a certain extent, symptoms can appear quite suddenly.
Accordingly, various attempts have been made to prevent such diseases before there is significant progression in organic pathological change, by determining the quality of circulation, the basis for these pathological changes. Accordingly, it has been the practice until now to determine the quality of circulation by focusing on risk factors such as blood pressure, changes in the electrocardiogram, blood cholesterol, neutral fat concentration, and the like.
However, in reality, it is not uncommon for cerebral apoplexy or heart failure to occur even in an individual with low blood pressure, while there are examples of elderly persons who have high blood pressure but still are in good health. Similarly, there are numerous instances where a substantial organic pathological change has occurred, but nothing is observed in the electrocardiogram, etc. While examination equipment may discover this change if it progresses further, this is not acceptable because of the additional delay.
Accordingly, the discovery that acceleration pulse waveforms can be useful as an indicator of the quality of circulation has gained attention in recent years. A brief explanation of acceleration pulse wave as a measure of circulation will now be provided. Namely, as is well known, circulation basically involves the heart pumping out blood, which flows through the arteries to the capillaries of the tissues and organs, and then returns through the veins.
The supply of oxygen and nutrients takes place at the capillaries, so that the quality of circulation is correlated to the behavior of the blood in the smallest vessels. Accordingly, transitions in the amount of blood contained in the capillaries may be viewed to serve as a good measure of circulation. Namely, a slight difference in arterial and venal blood pressure give rise to fine differences in nutrient supply and gas exchange at the capillary level. It is for this reason that it is believed that organic pathological changes may occur in tissues and organs if the difference in arterial and venal blood pressure expands over a long period of time.
Accordingly, one widely used method for observing changes over time in the amount of blood contained in the capillaries is the examination of the fingertip plethysmogram. However, the fingertip plethysmogram itself displays a gently undulating waveform. Accordingly, it was considered difficult to interpret very fine changes in the waveform. Further, there has also been the problem that changes in circulation are very small, and are sensitive to changes in the organism s environment.
However, if the second derivative of the fingertip plethysmogram waveform is obtained, to convert the waveform to a double differential plethysmogram (i.e., the acceleration plethysmogram waveform), it then becomes possible to enlarge and extract the information on circulation, and to display the circulation condition in a form which is easy to understand. FIG. 14(a) is one example of the original waveform obtained at the fingertip plethysmogram; FIG. 14(b) shows the waveform of the velocity plethysmogram obtained by taking the first derivative of the waveform shown in FIG. 14(a); FIG. 14(c) shows the waveform of the acceleration plethysmogram obtained by taking the second derivative of the waveform shown in FIG. 14(a).
FIG. 15 shows an example in which one waveform of a typical acceleration plethysmogram has been extracted. As shown in this figure, there are three peaks and two valleys in one waveform of an acceleration plethysmogram. Namely, there is an initial peak a, followed by valley b, peak c, valley d, and peak e. The waveform is roughly flat from peak e until the next peak a. Further, if peak a is excluded, then each point does not form a peak or valley, but rather simply becomes a point of inflection.
The significance of the amplitudes of each of the aforementioned peaks and valleys will now be described. To begin with, peak a is a signal that the blood pumped out from the heart has reached the capillaries in the fingertip. Valley b relates to the heart's stroke volume. The larger the stroke volume the deeper valley b falls.
Peak c is related to venal return, and, from the view of circulation, indicates whether or not there is excessive pooling of blood by appropriate contraction of venules. When the venal return is good, peak c is near or above the base line. In contrast, when blood pooling in venules is increasing, peak c ceases to rise, but rather falls below valley b.
Valley d is related to the load on the heart. When the load on the heart is increasing, valley d falls sharply. Peak e corresponds to the position of the rise in the fingertip plethysmogram after a contraction, however the concrete significance of this is not yet understood.
It is known that poor circulation as ascertained from acceleration plethysmograms as described above can be improved by jogging or other forms of endurance training. A temporary improvement may be noted from just a single training session, while a sustained improvement can be confirmed if training is continued. On the other hand, if training is suspended, circulation again deteriorates. Accordingly, it is possible to know the degree of improvement in circulation by analyzing the acceleration plethysmogram.
Japanese Patent Application First Publication No. Hei 8-10234 (Title: Device for Measuring Exercise Quantity) may be cited as one example of a technology which applies the above-described acceleration plethysmograms in exercise. This reference cites the use of a treadmill or bicycle ergometer for performing exercise to increase the health of the patient, with the exercise's effect on the patient measured. For this purpose, information referred to as "waveform representative values", which are calculated from the acceleration plethysmogram waveform, are measured before and after exercise, and the difference in these waveform representative values is displayed. Further, during exercise, the waveform representative values at each point in time are compared to predetermined waveform representative values. When the difference in the measured and predetermined waveform representative values reaches a value which is the patient's load limit, for example, then exercise is halted.
Japanese Patent Application First Publication No. 57-93036 may be cited as one example of an invention which attempts to determine circulation quality in a patient by analyzing the acceleration plethysmograms. Various sites such as the fingertip, earlobe, and the like may be considered for measuring the plethysmogram. However, the aforementioned reference specifically measures the fingertip plethysmogram. This is because the movement of blood from the arteries to the veins can be obtained at the fingertip, and because this is the site where the capillaries are most developed and the amount of blood contained therein is great. Moreover, the fingertip is ordinarily exposed, so that it may be freely brought near the plethysmogram measurement device. Accordingly, this enables a more simplified structure for the device.
The structure of the acceleration plethysmograph according to the invention in the above-cited reference is shown in FIG. 16. This device is formed by means of the cascade connection of a fingertip plethysmogram pick-up 200, pre-amplifier 201, operational amplifier 202, characteristic extraction circuit 203 which has two analog differentiating circuits utilizing CR circuits, and an oscillograph 204. Fingertip plethysmogram pick-up 200 is comprised of an opening 206 into which the patient inserts his finger, a light source 207, and a photoelectric element 208.
Three types of plethysmogram waveform graphs are displayed on oscillograph 204:
the plethysmogram waveform, and the first and second derivative waveforms of the plethysmogram which are calculated by characteristic extraction circuit 203. Accordingly, based on the acceleration plethysmograms shown on oscillograph 204, it is possible to determine the quality of circulation in the patient.
To begin with, as a first method for this determination, the acceleration plethysmogram waveform is typed according to the depths of valleys b and d into three categories: valley b&gt;valley d, valley b.apprxeq.valley d, or valley b&lt;valley d. Next, the thus-type patterns are further typed into three categories based on the height of peak c relative to the base line. The measured acceleration plethysmogram waveform is then set to whichever of these patterns it most closely resembles.
A second method of determination makes use of the height of peak c and the depth of peak d from the base line. As shown in FIG. 17, the depth of valley b is divided into four equal parts, for example, with the each partitioned area assigned a number 0, 1, . . . 5, in order from the base line. The number of points corresponding to the height of peak c, the depth of peak d, etc., are then determined from the positions thereof. In this way, the quality of circulation in the patient can be rendered as a numeric value.
This reference provides several working examples, including: 1) a device wherein, in place of a CR circuit, the measured value of the plethysmogram is digitalized using an A/D converter, and the acceleration plethysmogram is calculated by means of digital processing using a microcomputer; 2) a device wherein the third derivative waveform is obtained by taking the derivative of the acceleration plethysmogram waveform, and a microcomputer is used to obtain the position of the valleys and peaks; and 3) a device which corrects for fluctuations in the time interval of the plethysmogram due to respiratory action, by carrying out statistical processing, such as obtaining the arithmetic average for pairs of corresponding peaks and valleys, on the repeating waveform of a plurality of individual plethysmograms.
Japanese Patent Application First Publication No.: Hei 2-55035 discloses an invention which develops the above-described technology. The structure of the acceleration plethysmograph according to this reference is shown in FIG. 18. As shown in this figure, plethysmogram detector 300 includes a lamp 301 which is provided opposite the center of a concavity into which the fingertip is inserted, and a light detector comprising a photoelectric element 302. Photoelectric element 302 is formed of resistors 303 to 306 and a bridge circuit. The output from this bridge circuit is amplified by differential amplifier 307. Further, the brightness of lamp 301 can be adjusted with a switch S so that the bridge circuit is balanced. In this figure, the symbol V is the voltage of the electric source.
The output of differential amplifier 307 is amplified further by amplifier 308. Waveform correcting circuit 309 then modifies the amplified output to a rectangular waveform by clipping voltages which exceed a prefixed standard voltage. This output is differentiated at differentiating circuit 310, with micropulses generated in the negative direction by rectifier 311 to trigger one-shot multivibrator 312. As a result, a rectangular wave of duration T.sub.0 is obtained in the output of one-shot multivibrator 312.
In addition, the output of differential amplifier 307 passes through gate circuit 313 during an interval of the aforementioned duration T.sub.0. The output signal of gate circuit 313 passes through differentiating circuits 314, 315, with the output of the second derivative of the plethysmogram signal obtained in the output of differential circuit 315. Waveform correcting circuit 316 generates a sampling pulse for the output at each point in time where a valley b, peak c, and valley d appear. In accordance with this sampling pulse, sampling circuit 317 samples the output from differential circuit 315, which has passed through delay circuit 318, and stores the result in successive recording circuit 319. Maximum value detection circuit 320 reads out the contents of successive recording circuit 319, and records the maximum value from among the amplitudes for valley b, peak c, and valley d. The output of maximum value detection circuit 320 is divided at voltage dividing circuit 321, with each divided voltage then output.
Control circuit 322 successively outputs the voltages of valley b, peak c, and valley d, which are the output of successive recording circuit 319. This output is input into pulse height analyzer 323 which employs the output value of the voltage dividing circuit 321 as a comparison voltage, and, based on the voltages of valley b, peak c, and valley d, outputs values in which these voltages have been standardized (for example, ratios c/b, d/b, or ratios b/a, c/a, d/a, etc.) to output terminal OP.
A microcomputer or similar device determines which waveform pattern from among the pre-typed acceleration plethysmogram waveforms the waveform output at output terminal OP is associated with, and displays this result.
When making this determination of the waveform pattern, a determination is first made as to which of the voltage zones classified by voltage dividing circuit 321, the levels of standardized valley b, peak c, and valley d are associated with. For each of the separate voltage zones with which valley b, peak c, and valley d are associated, the measured plethysmogram is typed as one of the aforementioned patterns, based on the respective size relationship, and on the vertical relationship with respect to the base line of valley b, peak c, and valley d, to make a determination of the quality of circulation.
As explained above, maintaining good circulation is necessary to create a state of health. One important factor to accomplishing this is performing the appropriate level of exercise, to maintain a good circulation state for as long a period as possible. However, use of devices such as disclosed in the above-cited references present a problem.
Namely, it is known to be extremely difficult to accurately measure plethysmogram waveforms during exercise. Accordingly, using acceleration plethysmograms measured during exercise as a basis for controlling the exercise performed by a patient is not very successful, so that, as a result, the goal of carrying out the appropriate level of exercise is not achieved. Moreover, the present inventors carried out experiments using devices having the structures disclosed in the aforementioned references, and confirmed that plethysmograms could not be correctly measured. The same conclusion was reached even in the case where a sensor was attached to a patient's hand and the hand was held in place while the subject exercised on a tread mill, for example.
In devices such as those described above, information extracted from the acceleration plethysmogram is simply displayed to the patient. Thus, a doctor or nurse with special training is required to interpret these results. However, if numerous patients are exercising each day, and doctors and nurses must analyze the results and then direct the next exercise plan for each patient, then this creates a considerable burden on hospital personnel, and does not benefit the patient's treatment.
However, it is extremely troublesome and inconvenient for the user of the device himself to make a determination of the quality of circulation, without the assistance of a doctor or nurse. Moreover, there is no assurance that a patient exercising without a doctor present will be able to perform exercise of the same quality as would have been carried out if a doctor were present to provide guidance. Accordingly, when carrying out interval training or physical rehabilitation, various problems may occur, such as the exercise proving ineffective because it was too mild, or the exercise having an effect opposite that desired because it was overly strenuous.
On the other hand, guidance could be provided to the patient once every two or three weeks, but this is bothersome since it necessitates a visit to the doctor's office. Moreover, exercise of the same quality as if regular guidance were being provided still may not be carried out in this case. Accordingly, there have been grave doubts that effective exercise guidance could be carried out in the case where conventional devices were employed.